Abstract
Two new species of free-living marine nematodes from mangrove wetlands of Beihai, Guangxi province in China, are described and illustrated. Trissonchulus sinensis sp. nov. is characterized by a head continuous with the body, an amphidial fovea pouch-shaped, pharynx expanding gradually but not forming a posterior bulb, spicules sclerotized, blade-shaped, slightly curved ventrally, proximal part enlarged with a prominent central septum, posterior part slender and handle-like; gubernaculum small, composed of two distally connected sheet-like structures with tooth-like ends, and lacking apophysis. Metachromadora sinica sp. nov. is characterized by a cuticle that is finely annulated, labial sensilla papilliform, cephalic setae four in number, amphideal fovea loop-shaped, exhibiting a double-contoured appearance, pharyngeal bulb well-developed, internal cuticular lumen tripartite, lateral epidermal ridges present, spicules slender with an enlarged capitulum, gubernaculum boat-shaped, precloacal supplements absent, tail conical with two setose protuberances, three pairs of subventral preanal setae, and a pair of papillae situated anterior to the anus. Nearly full-length SSU sequences and D2-D3 of LSU sequences are provided for the new species. Phylogenetic analysis of SSU provided support for the current classification status of the two new species. In the SSU phylogenetic tree, the family Ironidae was recovered as a separate monophyletic clade. However, the phylogenetic relationships within the family Desmodoridae were complicated, and the subfamilies Desmodorinae and Spiriniinae were polyphyletic. A comprehensive taxonomic approach combining morphological observations and molecular phylogeny construction would be particularly valuable in a more robust nematode taxonomy.